Simulation Of Effect Of Biodiesel On Engine Combustion And Emission Under Multiple Injection Strategies

Biodiesel is a kind of clean and renewable energy, it is a good substitute for petroleum diesel because the physical parameters of most biodiesel and petroleum diesel are similar. The application of biodiesel is significant to solve the problem of energy shortage and environmental pollution. Reduced mechanism of diesel-biodiesel is built in this paper and coupling with three dimensional CFD simulation. The CFD simulation model is combined with diesel engine bench test to simulate the process of combustion and emission production of biodiesel mixed ratio 、 pilot injection strategy and post injection strategy, to investigate the effect of biodiesel on engine combustion and emission performance under multiple injection strategies when fueled with mixed fuel.At first, a reduced n-heptane mechanism is built from detailed n-heptane mechanism by using mechanism reducing method. Then we add methyl decanoate(MD)-methyl-9-decanoate(MD9D) reduced mechanism 、 GRI-NOx mechanism 、 PAH reduced mechanism to n-heptane reduced mechanism. Finally a 82 species and 314 reactions n-heptane-MD-MD9 D reduced mechanism is formed to replace diesel-biodiesel. The rationality of the reduced mechanism is verified by test data.In order to study the influence of mixed fuel blended ratio on the combustion and emission performance of diesel engine, we conduct the simulation of B00、B10、B20 and B50. Studies have shown that: Heat release peak decrease while ignition delay time extends with the rising blended ratio; NOx emission decreases as blended ratio rises; NO focus on high temperature region(T≥1700K) while NO2 focus on moderate-high temperature region(1000K≤T≤1700K), N2 O can be ignored because it is far less than NO;soot emission highly decreased as blended ratio rises and its oxidation process is majorly controlled by OH.We conduct the simulation to investigate the effect of multiple injection strategies on the combustion and emission performance of diesel engine when fueled with B20.Studies have shown that: Pilot injection makes the combustion process become gentler;NOx and soot emission both highly increase when compared to single injection, theydecrease with pilot-main interval increases and rise significantly with pilot mass increases;post injection makes NOx emission a little worse and its change does not much affect NOx emission; post injection can make soot emission significantly decrease; post injection is most favorable to soot emission reduction when main-post interval is between 10°CA and 20°CA while post mass is less than 6mg.